Extraction of ethylene from gaseous mixtures



Aug. 9, 1932. H z I EXTRACTION 0F ETI-IYLENE FROM GASEOUS MIXTURES FiledMarch 18, 1929 2 Sheets-Sheet l REGTI FIOATION 'COLUMN 9:16

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The present invention relates to the extraction of ethylene from gaseousmixtures containing ethylene, in particular from the gases from cokefurnaces to which the following description will, for the sake ofclearness, be directed, but only by way of example.

It is known that ethylene, or liqpids rich in eth lene, may be collectedin t e course of coo ing the gases from coke furnaces, before the mainliquefaction of its essential elements, methane, carbon monoxide andnitrogen. Such a process has been described in French Patent No. 585,996granted November 20, 1923, in which the liquefaction of the ethylene iseffected jointly with the rectification of the liquids formed, by thecirculation of these liquids in reverse direction to the gases arisingin the liquefaction zone. Carried out in this way, the liquid rich inethylene entrains in solution a certain amount of hydrocarbons or ofcondensible impurities which are liable to block the colder parts of theapparatus, and it is this liquid which is extracted outside.

In carrying into practice the process just.

referred to, it has been found that the elfect of rectification andwashin thus obtained may be insuflicient due to t e fact that thewashing liquid is only formed outside or inside the liquefaction tubes.This difficulty may certainly be remedied by replacing the liquefactiontubes by a rectification column traversed from below upwards by the asestreated, but difiiculties may then be found in suitably assuring, onaccount of the large exchange surfaces necessary, the cooling of suchrectification column by the separated. gases, hydrogen, nitrogen, carbonmonoxide, and methane, in the case of gases from coke furnaces.

The present invention has for its ob'ect to remedy in particular thisdefect and thus efiect an improvement in the process according to theabove mentioned specification.

The invention consists in collecting the liquid rich in ethyleneproduced by the cooling of the gases, with or without simultaneousrectification, and in placing the said liquid in intimate contact withthe gas remaining after this partial liquefaction; this contactfurnishing a gas which may be again cooled to liquefya further portionthereof. Furthermore, an improvement in the washing is obtamed by addingthis latter liquid to the first washing liquid, rich in ethylene,mentioned above. In these operations the success1ve coolings of the gasare obtained by causing them to circulate in indirect contact with thecold gases leaving the separating apparatus proper. The washing liquidsentrain practically the whole of the impurities, such as the acetyleneand the oxides of nitrogen which it was sought to eliminate; the cold ofthese liquids may then be simply recuperated or said liquids ma berectified to separate therefrom a gas re atively pure and rich inethylene, such rectification taking place, for example, through heatingby indirect contact with the gaseous mixture treated.

The accompanying drawings show in diagram, and as an example, anapparatus for carrying out the present invention. The two figures showrespectively the two portions of the apparatus out along line E-E.

In these drawings A and B are heat exchangers traversed successively bythe gaseous mixture to be treated, which arrives in a compressed stateat X, at the bottom of the exchanger A, and which is cooled in theseexchangers by the cold gases, leaving at low temperature the separationapparatus of the said gaseous mixture; this apparatus is not shown.

In the exchanger A are condensed principally water vapor and the partseasily liquefiable contained in the gaseous mixture treated, forexample, benzene. These liquids are collected in one or more fractionsand drawn off. In the exchanger B the circulation of the compressedgases takes place from the top to the bottom; the hydrocarbons of a hiher boiling point than methane, and a part 0% the methane itself, beingthere condensed and falling in a liquid state to the bottom part of B.The mixture of liquids thus produced passes through the pipe 4 to theupper part of the rectifying column C, while the compressed gaseousmixture leaving the bottom of the exchanger B passes by waof pipe 3 toand through the lower part 0 said column.

In columnC the ascent of this {gas and its descent in the reversedirection t from 4 cause the desired washing, and the uant-ity of thewashing liquid is increased by t e passage of the ases escaping from thetop of the colunm L into a nest of tubes D cooled as will be seen later.The purified gas-v eous mixture leaves from the top part at 5 to as intothe separation apparatus proper, and the liquid rich in ethylenecontaining also acetylene, oxides of nitrogen, and. other imurities, isdrawn off at t e lower part of C y means of a tube-1O provided with acock 11.

The nest of tubes is cooled at its lower part by the whole or a part ofthe methane or of the carbon monoxide or of the mixture of these gasesleaving the separation apparatus, which enters at 7 and leaves at 9, andat its upper part b the whole or a part of the hydrogen or o the mixtureof hydrogen and nitrogen coming from the same apparatus, whichcirculates from 6 to 8; these two streams of gases then passing throughthe heat exchangers B and A.

The liquid drawn off through the tube 10 generally contains a markedproportion of methane which has been condensed by the nest of tubes D.If the gaseous mixture obtained from the evaporation of the said liquidbe used, it is sent back to the proper compartment of the exchanger A torecover its frigidity.

But starting from the liquid in question a gas rich in ethylene may alsobe obtained by sending this liquid to the upper part of the rectifyingcolumn G after having expanded it b the cock 11 to the desired pressure.In its escent in G, the liquid meets the vapours comin from the liquidevaporated in the vaporizer E situated at the lower part of G. Thesevapours rise from E into G through a tube 13, while the liquid producedby the rectification descends from G into E through a tube 14. Therectification thus roduced furnishes on the one hand a gas ric inmethane,

which passes out at the upper part through valve 1 and may, for example,be joined to the methane leaving the separation apparatus proper, and onthe other hand a gas rich in ethylene, which leaves through a tube 15and passes, after having traversed a valve 16, to a compartment of theheat exchanger A. The column may be provided with other exits permittingthe separate collection of other elements constituting the ethyleneliquid treat ed; for example, a gas rich in ethane could be drawn offfrom an outlet tube 19. The vaporizer E is heated by the whole or a partof the compressed gaseous mixture treated on its passage between theheat exchangers A and B. The gaseous mixture leaving A arrives at 1,rises in the nest of tubes E, and leaves by the tube 2 to pass to theexchanger B. The liquids only s ightly volatile which accumuhe liquidlate in E are withdrawn through a purging cock 18.

What I claim is:

1. A method of extracting, by liquefaction, the ethylene inethylene-containing gaseous mixtures, which comprises the steps ofcoolin the gaseous mixture to liquefy substantia ly the whole of theethylene, thereby dissolving in said li uid a part of the acetylene andmtro en oxi es contained in said mixture, furt ier dissolving theremaining part of the acetylene and nitrogen oxides by circulatin theliquid obtained in said partial lique action in intimate contact with,and in the opposite direction to, the gaseous fraction remaining afterthe said liquefaction, separating the cold gases of said gaseousmixture, iquefying a art of the aseous mixture remaining after t efurther issolving operation in indirect heat-exchange with said.separated cold gases, and adding said liquefied part to the liquid richin ethylene obtained in the first liquefaction.

2. A method of extracting, by liquefaction, the ethylene inethylene-containing gaseous mixtures, which comprises the steps ofcoolin the gaseous mixture to liquefy substantia ly the whole of theethylene, thereby dissolving in said liquid a part of the acetylene andnitrogen oxides contained in the gaseous mixture, further dissolving theremaining part of the acetylene and nitrogen oxides by circulating theliquid obtained in said partial liquefaction in intimate contact with,and in the opposite direction to, the gaseous fraction remaining afterthe said liquefaction, se arating the cold gases of said gaseousmixture, liquefying a part of the gaseous mixture remaining after thefurther dissolving operation In indirect heat-exchange with saidseparated cold gases, adding t e liquefied part to the liquid rich inethylene obtained in the first liquefaction, and submitting the liquidresulting from the further dissolving operation to a rectification byheating it in indirect heat exchange with the gaseous mixture to betreated.

3. A method of extracting, by liquefaction, the ethylene inethylene-containing gaseous mixtures, which comprises the steps ofcooling the gaseous mixture by heat exchan with the se arated gases, soas to liquefy su stantially t e whole of the ethylene thereby dissolvingin said liquid a part of the acet lene and nitrogen oxides contained insaid mixture, further dissolving the remaining part of the acetylene andnitrogen oxides by circulating the liquid obtained in said partialliquefaction in intimate contact with and in the opposite direction tothe gaseous fraction remaining after the said liquefaction, separatingthe gaseous mixture into its constituents by liquefaction, liquefying aart of the aseous mixture remainin after t e further issolving operationin indirect heat exchange with said separated constituents, adding saidliquefied part to the liquid rich in eth lene obtained in the firstliquefaction, recti ying the liquid resulting from the furtherdissolving operation while utilizing the gaseous mixture as a heatingagent in said rectification, and circulating in indirect contact withthe gaseous mixture the ethylene resulting from said rectification andthe separated gases which have been used to cool the gaseous mixture andthereby liquefy substantially the whole of its ethylene.

In testimony whereof I afiix my signature.

HENRI LANTZ.

